Scribner's panic grass is a plant of dry woodlands, known from widely separated sites in southeastern and northwestern Montana. Only one large-sized population is known in the state, two others are very small, and the fourth occurrence is known only from a historical collection. Occurrences in eastern Montana may be negatively impacted by cattle grazing. The largest occurrence in the state lies adjacent to Highway 93 and negative impacts associated with expansion of the highway is likely. Invasive weeds and forest encroachment are also problems at this site.

General Description

Scribner's Panic Grass is a perennial which forms clumps of simple or branched stems that are 1-6 dm tall. The lower leaves are 3-10 cm long and 3-12 mm wide, while the upper leaves are short and relatively broad. Leaves are mostly glabrous, but the sheaths surrounding the stem are glabrous to long-hairy. There is a short fringe of hairs on the leaf where it meets the stem, which is known as a ligule. The flowers are borne on short to long stalks, which are arranged in a conical inflorescence that is 3-8 cm high. Inflorescences of the main stems are larger than those of the branches. Each egg-shaped spikelet has one flower, is ca. 3 mm long, and consists of two glumes enclosing a lemma and a palea that may or may not be hairy.

Phenology

Spikelets mature in late June and early July.

Diagnostic Characteristics

The relatively large, egg-shaped, single-flowered spikelets help identify this as Dichanthelium (formerly part of the genus Panicum). Panicum virgatum is rhizomatous with spikelets that are about 4 mm long, and Panicum capillare is an annual. Spikelets of D. occidentale (= D. acuminatum) are about 2 mm long. Montana plants are var. scribnerianum, as var. oligosanthes occurs only in the eastern U.S.

(Observations spanning multiple months or years are excluded from time charts)

Habitat

This plant has been documented from southeast and northwest Montana. In Lake County it was collected in sandy pinelands. Two small colonies recently documented in Powder River County occupied Pinus ponderosa/Mahonia repens habitat. Both were at the upper end of draws, with one on the lower south-facing slope of a steep, wooded drainage and the other at the gently sloping upper end near the border between woodland and grassland. Associated species included Agropyron spicatum, Astragalus agrestis, Astragalus americanus, Carex deweyana, Carex sprengelii, Crepis acuminata, Elymus glaucus, Euphorbia glyptosperma, Penstemon gracilis and Poa pratensis. Soils were well-drained, coarse, sandy or gravelly loams.

Scribner's panic grass is a perennial that reproduces strictly by seed. Both vernal (early season) inflorescences and autumnal (late season) inflorescences are produced. The species survives fire, but impacts on population size are unknown. In one locality that had burned, plants emerged earlier and had more stems than those at a nearby unburned site. This species does not exhibit marked population increases in the wake of fire, as does Wilcox' panic grass (Heidel and Dueholm 1995).

Management

Areas of Lake County where this grass occurs are being invaded by knapweed species. Many wooded draws in southeastern Montana are being invaded by leafy spurge. This panic grass is thought to decrease under grazing (Smith 1976), and overgrazing could adversely affect it.